The present invention relates to the field of flat-bottom bags, and more particularly, to processes for manufacturing the same.
Flat-bottom bags are well-known in the prior art. Such flat-bottom bags are commonly constructed of tubes of paper, closed at one end in accordance with any of a multiplicity of known processes.
The steps of one such known process are illustrated in FIGS. 1-2B of U.S. Pat. No. 5,314,252 (Happ), issued May 24, 1994. In this process, opposite sides of a tube end are folded in to leave flap portions (this configuration is typically referred to as a full diamond fold configuration), and a layer of adhesive material is applied, as shown in FIG. 1. Thereafter, rotary folding clamps, also known as front and back jaws (not shown), fold the flap portions, in sequence, against the folded-in portions, whereupon they are adhered in place by the adhesive. This forms a bag, as shown in FIGS. 2, 2B, that is quite suitable for use, for example, as a grocery bag. However, such bag, when used for the containment of particulate material, such as flour or sugar, has been found to be susceptible to leakage.
Accordingly, attempts have been made in the prior art to avoid such leakage.
Several such attempts, in the nature of variants of the foregoing process, are described in the Happ reference.
As one variant, illustrated in FIG. 3 of the Happ reference, a patch is adhesively attached to the bag bottom. This reduces migration of particulate materials, thereby rendering the bag relatively more suitable for use therewith. However, leakage can persist at problematic levels. Further, the external patch is susceptible to partial detachment, which detracts from aesthetics of the bag.
As another variant, illustrated in FIG. 4 of the Happ reference, the bag is formed of two ply material, and provided with a staggered slit, such that the outer ply forms an integrated patch. This improves aesthetics. However, leakage can still persist at problematic levels.
Another known process is described in U.S. Pat. No. 5,913,764 (Kolbe et al.), issued Jun. 22, 1999. In this process, a patch is provided interiorly of a bag of the full diamond configuration. This process is taught to lessen leakage, and provides aesthetics identical to other full diamond bags. However, it suffers from the need to employ contact adhesives, thereby rendering it unsuitable for adaptation to many existing bag-forming lines.
It is also known to practise the Kolbe et al. process in conjunction with bags of the staggered slit variety. This process is similarly known to lessen leakage, and to provide aesthetics identical to other staggered slit bags. However, it continues to suffer from the need to employ contact adhesives.
It is an object of the invention to provide a process for manufacturing a relatively leak-proof flat-bottom bag which does not suffer from the need to employ contact adhesives.
This object, amongst others, is met by the present invention, a process for manufacturing a flat-bottom bag.
According to one aspect, the process comprises the step of providing a bag preform and a patch.
The patch has a first adhesive coating thereon.
The preform is formed from an elongate tube of bag-forming material, said tube comprising an inner tubular liner of bag-lining material sheathed by an outer tubular shell of bag-facing material and having a peripheral baseline which divides said tube into a tubular wall-forming part including a preform upper end and a tubular bottom-forming part including a preform lower end.
The bottom-forming part has four division lines, running lengthwise, along the length of the tube, which divide said bottom-forming part into four substantially rectangular bottom-forming portions including a pair of substantially congruent flap-forming panels and a pair of substantially congruent gusset panels, disposed in alternating relation.
One of the flap of forming panels has a staggered slit arrangement including a pair of relatively long first slits and a pair of relatively short second slits. The first slits are formed through the shell, extend from the preform lower end, lengthwise, to respective termini and are arranged such that each of the division lines which bracket said flap forming panel has a respective one of the first slits disposed relatively proximal thereto. The second slits are formed through the liner, extend from the preform lower end, lengthwise, to respective termini and are arranged such that each of the division lines which bracket said flap forming panel has a respective one of the second slits disposed relatively distal thereto.
Each flap-forming panel has a pair of flap-forming creases associated one each with the division lines which bracket said each flap-forming panel and each extending in angular relation to its associated division line and from the intersection thereof with the peripheral baseline to,
with respect to the other one of the flap-forming panels, the preform lower end, so as to divide said flap-forming panel into a quadrilateral flap and a pair of opposed triangular gussets; and
with respect to said one of said flap-forming panels, the terminus of a respective first slit, in the case of the shell, and the terminus of a respective second slit, in the case of the liner, so as to divide said flap-forming panel into a ridged flap and a pair of opposed polygonal gussets.
The preform is provided in an open configuration. At the open configuration, the triangular gussets and the polygonal gussets are folded inwardly along the flap-forming creases contiguous therewith such that the division lines are arranged substantially coincident with the peripheral baseline, thereby to form, with the quadrilateral flap and the ridged flap, respectively, primary and secondary flaps. Further, the primary and secondary flaps extend substantially away from one another, such that the triangular gussets and the polygonal gussets form substantially smooth continuous surfaces with the gusset panels to which they are respectively attached.
The method also comprises the step of positioning the patch at a sealing position against said smooth continuous surfaces, with the first adhesive coating disposed therebetween, to form a preform/patch composite.
The method also comprises the steps of: folding the primary flap about the peripheral baseline to a closure position thereof whereat same lies in substantially stacked relation relative to the gusset panels; folding the secondary flap about the peripheral baseline to a closure position thereof whereat same lies in substantially stacked relation against the primary flap; and providing means for securing the primary flap and the secondary flap at their respective closure positions.
As another aspect, the invention also comprises a bag formed in accordance with the foregoing process.
Other advantages, features and characteristics of the present invention will become apparent upon consideration of the following detailed description and the appended claims with reference to the accompanying drawings, the latter of which is briefly described hereinafter.